This invention relates to electrostatographic printing machines, and more particularly this invention relates to an electrostatographic printing machine that performs transfuse of a toner image to a substrate.
Electrostatographic printers are known in which an image bearing member is used to develop multiple color toner images. Each color toner image is electrostatically transferred in layers from the image bearing members and registered to an intermediate transfer member. The composite toner image is electrostatically transferred to the final substrate. Such systems use electrostatic transfer to transfer the composite toner image from the intermediate to the final substrate and then subsequently fix the image on the substrate in a fusing system.
For example, with reference to commonly-assigned U.S. Pat. No. 6,088,565, the disclosure of which is incorporated herein by reference, electrostatographic printing machine is disclosed having multiple toner image producing stations, each forming a developed toner image of a component color. The developed toner images are electrostatically transferred at the first transfer nip to an intermediate transfer member to form a composite toner image thereon. The composite toner image is then transferred electrostatically and with rheological assist at the second transfer nip to a transfuse member. The transfuse member preferably has improved conformability and other properties for improved transfusion of the composite toner image to a substrate. The second transfer member is maintained at a selected temperature relative to the glass transition temperature of the composite toner image at the second transfer nip. The composite toner image and the substrate are brought together in the third transfer nip to generally simultaneously transfer the composite toner image and fuse the composite toner image to the substrate to form a final document.
The use of an intermediate member allows electrostatic transfer in the first transfer nip to suppress transfer of background toner from the image bearing member. The intermediate transfer member can be selected to have a low affinity for receiving background toner.
In addition the intermediate transfer member thermally isolates the image bearing member from the heat of the transfuse member. Therefore the transfuse member can operate at a relatively higher temperature without the potential to damage the image bearing members. Because the transfuse member can be maintained at a higher temperature, the transfuse member can be relatively thick.
Thick transfuse members are generally preferred over thin members for a number of reasons. For example release of melted toner and stripping of a copy sheet from a toner fixing surface can be significantly helped by employing shear stresses in the fixing surface in the high pressure third transfer nip that are generally referred to as xe2x80x9ccreepxe2x80x9d. A thick rubber over layer is also desired for creating a high degree of conformance to enable good transfer and fix in the third transfer nip when rough papers are used. A thick transfuse belt thus generally has more media latitude than a thin transfuse belt. Thick transfuse members are also desired over thin members for achieving higher operational life. Finally, thick over layers are highly advantaged for transfuse systems that achieve low gloss in the third transfer nip and employ an optional post transfuse gloss enhancing system to allow operators to optionally choose high or low gloss print output.
However, efficient and uniform heating of a thick transfuse member can be difficult.